There are three major objectives: First, to explore diaphragm pacing by electrical stimulation of the phrenic nerve as a method of artificial respiration in the treatment of certain patients with chronic ventilatory insufficiency including respiratory paralysis (quadriplegia), central alveolar hypoventilation (CAH) and chronic obstructive pulmonary disease (COPD). Investigations are designed to aid in the selection of patients for pacing and in the evaluation of the results. They include studies on respiratory control, airway resistance and hemodynamics. Second, to investigate newly developed electronic apparatus of diaphragm pacing including a totally implantable diaphragm pacemaker, a hermetically sealed capsule for electronic components, a demand diaphragm pacemaker, and a new electrode design. Third, to investigate ways to extend the safe period of continuous ventilatory support by diaphragm pacing. Tests designed to reveal the influence of altering physical and electronic parameters on the effectiveness of pacing will be employed.